Honest questions. What is “story now” and how is 4E an example of it?
"Story now" is a label used to describe an approach to RPGing where (i) the goal is that play should produce a story in the standard sense of that word (ie not just a series of connected events, but something with rising action, climax, character development, thematic significance, etc), and (ii) that first goal is to be achieved with no one having to actually write a story.
It contrasts with (i) story before - where someone (typically the GM or the module author) writes the story which the players play through - and with (ii) story after - where there can be war stories after the event, but play itself does not have those characteristics of a story. (A lot of wargaming can produce these sorts of war stories; but wargaming is not a "story now"-oriented hobby.)
The phrase "story now" comes from Ron Edwards and The Forge. Another label used for the same thing is "narrativism" - but on these boards (ie ENworld) "narrativism" is normally used to mean "story before" and so that term can be a source of terminological confusion.
The phrase "story now" is coined in the early 2000s. One of the first games written to be played in this sort of fashion - and predating the label by more than a decade - is Greg Stafford's Prince Valiant. But Edwards has always emphasised that this sort of play was happening using other systems not specifically written to support it - sometimes this gets labelled "vanilla narrativism". Ie playing story now without any fancy mechanical trappings. I've done this sort of play using AD&D: OA and an all-thieves campaign. I mention those details because they're pretty relevant: OA characters, and thieves, bring "baggage" and context/connections to the setting and situation that generate a drive/trajectory for play that not every AD&D character does, and that sort of drive or trajectory is necessary for story now play to happen.
I've also used RM for "vanilla narrativist" play. But these days I wouldn't go to RM or AD&D for this sort of RPGing because I know systems that are better suited and don't have mechanical aspects that get in the way.
4e supports "story now" play pretty well because most PCs bring thematic heft/trajectory (not all - archer rangers are a bit of an energy sink by default), it has mechanics that strongly encourage players to proactively engage the system, it uses scene-based resolution which supports pacing and stakes-setting (necessary for rising action, climax, theme, etc), and at every point where traditional D&D has favoured GM-driven "story before" (adventure hooks; deciding what the treasure is; etc) 4e encourages a player-driven approach instead (player-authored quests; magic item wishlists; etc).
A fuller discussion of some of this is in this old thread:
D&D 4E - Pemertonian Scene-Framing; A Good Approach to D&D 4e